An interlaboratory study in which 20 laboratories participated was conducted to provide precision and accuracy statements for the proposed EPA Method 612 - Chlorinated Hydrocarbons for measuring concentrations of the Category 3 chemicals hexachloroethane, hexachlorobutadiene, 2-chloronaphthalene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, hexachlorobenzene, and hexachlorocyclopentadiene in municipal and industrial aqueous discharges. Hexachlorocyclopentadiene was eliminated from the study because of its instability in the solvent used to prepare sample concentrates. The study design was based on Youden's plan for collaborative tests of analytical methods. Three Youden pair samples of the test compounds were spiked into six types of test waters and then analyzed. The test waters were distilled water, tap water, a surface water, and three different industrial wastewater effluents. The resulting data were statistically analyzed using the computer program entitled 'Interlaboratory Method Validation Study' (IMVS). In all cases, there was no evidence of a statistically significant effect on accuracy or precision due to water type.